The referenced publication "Bosch Technische Berichte" ("Bosch Technical Reports"), vol. 5, 1977, issue 5/6, page 253, describes an electronic ignition system which includes a microprocessor. The microprocessor receives input signals representative of engine speed, engine loading, and other signals, for example temperature, indicating whether the engine operates under starting conditions or the like. The computer--typically a microprocessor--then provides output signals representative of ignition instant, duration of current flow through an ignition coil, speed threshold levels and the like. To furnish the output data, a memory is provided which retains therein tables or other data specific to the vehicle and/or engine being used. These data are stored in a programmable read-only memory (PROM) which is interrogated by the computer to obtain the relevant data on which the computation can then be based.
It is well known that computers of this type utilize integrated circuits to be inserted in sockets. The arrangement should be such that, first, a readily programmable, typically an electrically erasable programmable read-only memory (EPROM) can be inserted in the respective socket, to be later on replaced by a non-erasable PROM. The system permits changing the data in the EPROM until the respective data stored therein are optimally matched to the desired performance upon computation in the microprocessor based on the data in the EPROM. These data, when they are found optimally suitable, are then transferred into a PROM, that is, a memory which is no longer erasable. The PROM could subsequently also be exchanged, for example due to a defect or if a specific data block therein should be changed.
Various types of computer arrangements use hybrid circuit technology. Integrated circuit (IC) chips, not yet packaged or irremovably encapsulated, are secured to a ceramic or ceramic-like substrate. Connections from the IC chips are then made with conductive tracks, formed in thick-film technology on the substrate material, by suitable connection of bonding wires between the terminals of the IC chips and the conductive tracks. Such hybrid circuits permit particularly compact design and construction. They are very light, and the low weight, and hence inertia, permits high mechanical loading thereof. No insertion terminals, for example plug-and-socket connections, are used. Such plug-and-socket connections frequently are the source of malfunction. The IC hybrid technology, thus, has a higher degree of reliability. Hybrid technology IC circuits are thus used increasingly not only in control systems for aircraft, but also for automotive-type or other vehicular control systems. Automotive-type control systems are subject to severe operating conditions: extremes in temperature variations, high mechanical loading, vibration, shock, and the like.
Use of non-packaged or raw PROM--IC chips has the disadvantage that these chips can be programmed only after the chip is secured and assembled with the remainder of the substrate, that is, only when the chip is connected by the bonding wires. Thus, any errors or malfunction in the PROM--IC chip cannot be detected until the PROM--IC chip is secured to the substrate, and the overall computer apparatus with the respective PROM--IC chip has been completely assembled and wires, including the connection of the bonding wires. Erroneous programming, also, cannot be detected before the PROM--IC chip is assembled. Exchange of an erroneously programmed or malfunctioning chip is not economically feasible and, in many situations, may not be possible. Thus, if there should be an error, a malfunction, or other defect in the PROM--IC chip, carrying the data, the entire hybrid circuit has to be scrapped.